Study On The Influence Of Combustion Of Multiple Fuels In Different Physical States On Engine Emission And Performance

Emission is an important indicator of engine performance.Using alternative fuel is an effective way to reduce engine emission.The mixed use of multiple alternative fuels can ensure the emission performance of the engine,by reasonably selecting the fuel and blending ratio and optimizing the parameters of engine fuel injection.Usually,alternative fuels are more economical than traditional fuels.Therefore,based on research and analysis of the research background,significance,and development status of multi-fuel engines,the theory and methods for determining the optimum blending ratio of multiple fuels in different physical states are studied,multi-fuel engine emissions and performance at optimum blend ratio are also studied,and the velocity and turbulent kinetic energy in the intake and in the cylinder of the multi-fuel engine at optimum blend ratio during the intake process are analyzed.The specific work is as follows:Firstly,according to the main structure parameters of the original machine,the engine geometry model and grid model were established respectively using CATIA and ICEM software.According to the idea of uniform design,a uniform experiment of 15 different working conditions was designed.The distribution of multi-fuel blending ratio was achieved by allocating the fuel-air ratio.The finite volume method and dynamic grid technology were used to numerically simulate the multi-fuel engine with FLUENT.The engine torque values and CO,NOx,HC,and Soot emissions for 15 different operating conditions were obtained.Secondly,using the scoring method,the weights of torque,CO,NOx,HC,Soot,and various functional indexes under three conditions of low-speed medium load,medium-speed medium load,and high-speed medium load are determined.According to the basic principles of value engineering,the cost coefficient and function coefficient of the three working conditions are calculated,the value coefficient is obtained,and the best proportion of the mixed burning under three working conditions is obtained.Using the optimal blending ratio for each of the three conditions,the engine load was selected to be 50%,and the dynamic performance and emissions of the multi-fuel engine and the original engine were compared.The torque was slightly worse than that of the original machine,but the power loss was not significant.CO,NOx,HC,Soot emissions havebeen improved compared to the original machine,and emission performance has improved.Finally,by analyzing the velocity field and the turbulent kinetic energy field in the intake and the cylinder during the intake process,the vortex changes in the intake and the cylinder during the intake of the engine are obtained.Two vortexes with higher flow velocities are formed on both sides of the intake valve rod and vortexes with smaller flow velocity are formed below the intake valve rod,which play a very favorable role in the mixing and combustion of the gas in the engine cylinder.